The commercial drying of seed corn is relatively well-developed art. It differs from the drying of feed corn in that it must be more precisely controlled since the moisture content of the kernels of corn for best removal from the ear is critical and overdrying must be avoided in order to avoid damaging the kernels so that they will withstand storage until they are planted, and so that they will have good emergence and growth characteristics.
There are two well-known methods of drying seed grain, such as seed corn, which are known as the bin-layer dryer method and the batch-in-bin method. The former utilizes a bin to which a duct is led which has a fan and a heater unit, and the system dries the granular material by forcing heated air through a perforated bottom floor of the bin and upwardly through the successive layers of the granular material which have been added to the bin, thereby absorbing moisture and thus reducing the moisture content of the seed material in the bin.
Obviously the layers placed in the bin early in the operation will be reheated several times during the drying of the layer added later. Moreover, this bin layer dryer system requires a substantial amount of time to dry a full bin of granular material, and there is always the danger of overheating or overdrying the material in the lower layers.
The batch-in-bin dryer system is an improvement on the bin layer dryer method, and in this method a single layer is dried on the perforated floor of the dryer bin, by passing the heated air through the layer and then the dried material is transferred to a storage bin. In more recently built systems of this type, the flow of the heated air may be reversed, i.e. being passed from the top of the bin down through the granular material in the bin and out through the perforated bottom 4. This overcomes the disadvantages of the bin-layer dryer method in that each batch is subjected to drying only once. However, one of the disadvantages of this system is that an entire batch must be dried before any of it can be removed or replaced by a new batch.
Moreover, both of these systems, in actual practice, are operated with a plurality of bins in parallel and housed in a single building with large passages therethrough for the gaseous drying medium. Each bin is filled, and then the heated air from a single source of heated air consisting of a heater and a blower is directed in parallel through the bins. Manifestly, this requires a large capacity heating system and blower system, and a relatively strong building to withstand the rather high air pressures generated by such a large blower system. The passages into the respective sections are provided with dampers. Therefore, if the seed material, for instance seed corn, which is coming from the fields, is not sufficient to fill all of the bins in a particular section of the building in which the bins are housed, the excess heated air passed through the filled, partially filled, or unfilled bins is not utilized, and heat is thus wasted.
Further, the fuel utilized in heating the air has generally been natural gas or the like, which is simply burned in the ambient air and drawn immediately into the blower for distribution to the various systems of bins. Natural gas has heretofore been readily available at a low price, and since it produces a very clean product of combustion, it is well-suited to the heating of air for the purpose of drying seed materials.
Natural gas does have the disadvantage that it produces amounts of water vapor as products of combustion which have some significance in the overall drying operation, particularly seed corn, since this amount of water vapor is relatively large in comparison to the amount of water vapor removed from the seed material. However, the cost of natural gas has heretofore been so low that this disadvantage is not so significant that efforts to overcome it would have been justified from an economic standpoint.
More recently, efforts have been made to provide dryers for granular agricultural products which are similar to continuous flow dryers for particulate material, but which nevertheless handle the agricultural materials one batch at a time, although they are automatically fed into the dryer structures and automatically removed therefrom. One such apparatus is disclosed in U.S. Patent 3,634,949 to Robert A. Louks. In this apparatus, a cylindrical housing is provided with a downwardly directed cone having a perforated wall portion at the lower part thereof, and a second smaller perforated cone is positioned within the first cone near the bottom thereof to define an annular conical space therebetween. Grain is fed into this space, and in the actual Louks arrangement, which is a true continuous-flow dryer, as the grain moves down the space to the bottom of the outer cone, warm air is forced across the annular conical space through the perforated wall portions to dry the grain moving along the cones.
While this apparatus is readily adaptable for drying such grains as feed corn, it does not permit the rapid emptying and self-cleaning required in the drying of seed grain, and particularly seed corn in the ear.
Moreover, in this apparatus, the source of fuel for heating the air for the drying operation would still be a natural gas or the like, since the air is directed directly from the heater and the blower through the system into the cylindrical housing.
Among various steps taken to overcome the recent problem of the decreasing availability of natural gas as a drying medium, efforts have been made to burn the cobs from which the seed corn has been shelled as the fuel for heating the air used as the drying means for the seed corn. These efforts have involved placing the gaseous products of combustion from the cob directly into the air to be heated, i.e. mixing the gaseous products of combustion and the ambient air to form a gaseous drying medium, and directing this drying medium over the corn, either in the conventional drying bins or in the bins which are set up in the form of a continuous dryer.
The heat content of the cobs is just about sufficient for the drying of the seed corn by the conventional drying method and apparatus now available in the art. It has been found that in the conventional method and apparatus, particularly the batch-in-bin method and apparatus, the amount of heat necessary per bushel of corn dried from the normal moisture content as it comes from the field to the desired moisture content for shelling, namely from about 30% to a range of from 12-13%, is 70,000 btu per bushel. This is substantially the same amount of heat which can be obtained from burning the cobs from which the bushel of seed corn has been removed. It therefore appears that if all of the heat from the cobs can be added to the drying medium, it will be possible to obtain a successful method and apparatus in which all of the fuel necessary for drying the corn is obtained from the cobs.
However, this solution of the fuel problem is not believed to be a workable solution. In the first place, particulates are added to the gaseous drying medium from the combustion of the cobs, and while the larger particulates can be readily removed by conventional equipment, the smaller particulates are rather difficult to remove without rather high costs for equipment and operation. In many of the installations, particularly the bin-type installations described above, personnel work in the air tunnels closing and opening the dampers to the passages leading to the bins to control the flow of the drying medium. There can be no assurance that the particulate levels in the drying medium will be such as not to injure these personnel.
More important, however, it has been found that the particulates produced during the combustion of the cobs are high in potassium, and when these particulates are directed onto the seed corn, it is believed that they may damage the emergence characteristics of the seed when the seed is planted.
Thus, since the direct mixing of the products of combustion of the cobs into the drying air, which is the only way to add all of the heat of combustion to the drying air, can cause damage both to the personnel operating the systems as well as to the corn itself, it appears that a method and apparatus in which the cobs are utilized for the entire amount of fuel necessary to dry the corn cannot be used. In fact, it appears that even if the danger to personnel could be overcome, for example by the use of gas masks or rearranging the controls for the dampers, nevertheless the burning of cobs and the heating of the drying medium in the conventional manner from the products of combustion of the burning of the cobs should be avoided due to the possible damage of the seed corn with respect to its emergence characteristics. It would thus seem that only indirect heating of the gaseous drying medium would avoid the problems of direct heating, and of course this involves a heat loss which means that the cobs will not serve as the source of all the heat needed.
Another aspect of the problem of burning the cobs is that while cobs are an economical source of heat, they are also a marketable item. However, there is a by-product of seed corn production which is unmarketable, namely unsatisfactory seed corn. By this term is meant seed corn which is no longer sufficiently fresh to germinate with the desired consistency, i.e. outdated seed corn, and seed corn which is found after processing to germinate unsatisfactorily even though freshly dried. Such corn is estimated to be about 5% of any given crop of seed corn. Such corn cannot be sold for animal feed, since it has been treated with fungicide and the fungicide cannot be sufficiently completely removed to make such corn acceptable as a feed. Such corn can however be burned without impermissible atmospheric contamination.
It would therefore be a significant advance in the art to have a method and apparatus which can obtain all of the fuel necessary for the drying operation from the cobs and the unsatisfactory seed corn, and nevertheless avoid the problems of particulates in the drying medium, both from the standpoint of lack of danger to the operating personnel and avoidance of contact of the potassium containing particulates with the seed corn being dried.